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UBC Theses and Dissertations

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UBC Theses and Dissertations

A System for the efficient automated analysis of reconstructed double-pulsed holograms Zhao, Zhijun

Abstract

Double-pulsed holograms of particles in a flow form the basis of Holographic Particle Image Velocimetry (HPIV), which is becoming widely used for the measurement of three-dimensional velocity fields. The major deficiency of HPIV is that the double-pulsed holograms must be surveyed by a human operator, at a considerable cost in time and effort, to determine the location of objects within the holographic volume. A system that automatically and efficiently analyzes double-pulsed holograms of microbubbles in flowing water has been developed. The system employs a three-part algorithm: 1.Holograms of microbubbles are scanned in the holographic (x-y) plane using acomputer-controlled positioning table. Microbubbles within the scanned regionare detected by a CCD-based fast object detection system. On detection of a probable bubble signal, the CCD board signals the computer to stop scanning. 2.Bubble images thus detected are focussed (in the z-direction) using a software-based auto focussing technique. 3. In-focus bubble images are analyzed by a simple set of image analysis techniques, including edge detection and patch correlation. The output of this algorithm is the size, and displacement between the two laser pulses, of microbubbles in the water flow. Large numbers of experiments were conducted using this algorithm. On the basis of these experiments it is concluded that scanning the large empty regions ofspace in a hologram to identify the widely separated microbubbles (step 1 above) can be done at almost the human rate. In contrast, the second part of the algorithm — autofocussing of bubble images with the present hardware — requires more time than does a human operator. The third part of the algorithm, involving automated bubble image analysis, can be carried out at very nearly the human rate.

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